Abstract
Purpose
The effect of isoflurane on the subcortical P14 component of the median nerve somatosensory evoked potential (SEP) is poorly known. We studied whether the P14 wave from the upper brainstem, recorded with a nasopharyngeal electrode, was attenuated at the isoflurane-induced EEG burst-suppression level. We also compared the effect of isoflurane on the P14, cervical N13 and cortical N20, N35 and N60 components.
Methods
Seventeen elective patients were anaesthetized with isoflurane. Somatosensory evoked potentials were recorded pnor to anaesthesia, at 0.5 MAC and I MAC end-tidal isoflurane as well as at the level when EEG was in burst-suppression (mean 1.9 vol% end-tidal isoflurane).
Results
Isoflurane had varying effects on the subcortical components of median SEP. The amplitude of nasopharyngeal P14 was stable, but the mean latency increased from 14.4 ± 1.2 msec at 0.5 MAC to 15.2 ± 1.1 msec at burstsuppression level (P < 0.05). In contrast, the N13 neck response amplitude was attenuated from 3.3 ± 0,6 μV to 2.6 ±0.5μV (P < 0.005) without latency changes. The latency of the cortical N20 wave was increased from 19.7 ± 1.1 msec at awake to 24.4 ± 1.6 msec at burst-suppression level (P < 0.0001) and amplitude was reduced from 3.3 ± 1.1 μV to 1.3 ± 0.6 μV (P < 0.0001). The later cortical components were attenuated even during 0.5 MAC isoflurane and were not recordable during EEG burst-suppression.
Conclusion
We conclude that P14 can reliably be recorded with nasopharyngeal electrodes during isoflurane anaesthesia, even during EEG burst-suppression, when the N20 wave is attenuated. In contrast, the middle-latency SEP components are sensitive to isoflurane anaesthesia.
Résumé
Objectif
Nous connaissons mal l’action de l’isoflurane sur la composante sous-corticale P14 du potentiel somatosensoriel évoqué (SEP) du nerf médian. Nous avons cherché si l’onde P14 enregistrée à la partie supérieure du tronc cérébral avec une électrode nasopharyngée diminuait lorsque l’isoflurane ralentissait l’ÉEG jusqu’au niveauburst-suppression. Nous avons aussi comparé l’influence de l’isoflurane sur les composantes P14, cervicale N13 et cortkales N20, N25 et N60.
Methodes
Dix-sept patients électifs ont été anesthésiés à l’isoflurane. Les potentiels évoqués somatosensorielsont été enregistrés avant l’anesthésie, à 0,5 MAC et à 1,0 MAC télé-expiratoires et au niveau deburst-suppression ÉEG (concentration télé-expiratoire 1,9% d’isoflurane).
Résultats
L’isoflurane avait des effets variés sur les composantes non-corticales des SEP médians, L’amplitude du P14 nasopharyngé était stable, mais la latence moyenne augmentait de 14,4 ± 1,2 ms à 0.5 MAC à 15 ± 1,1 ms pendant leburst-suppression (P < 0,05). Par contre, l’amplitude de la réponse N13 cervicale était atténuée de 3,3 ± 0,6 μV à 2,6 ± 0,5 μV (P < 0,005) avec une latence inchangée. La latence de l’onde corticale N20 augmentait de 19,7 ± 1,1 ms a l’etat vigile à 24,4 ± 1,6 ms pendant leburst-suppression (P < 0,0001). Les demières composantes corticales diminuaient même sous isoflurane 0,5 MAC et n’étaient pas enregistrables pendant leburst-suppression à l’ÉEG.
Conclusion
Nous concluons qu’il est possible d’enregistrer P14 fidèlement avec des électrode nasopharyngées pendant l’anesthésie à l’isoflurane, meme pendant leburst-suppression lorsque l’onde N20 est atténuée. Par contre, les composantes SEP de latence moyenne sont sensibles à l’anesthésie à l’isoflurane.
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Supported by grants from the Scientific Research Fund of Tampere University Hospital and the Emil Aaltonen Foundation.
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Porkkala, T., Kaukinen, S., Häkkinen, V. et al. Median nerve somatosensory evoked potentials during isoflurane anaesthesia. Can J Anaesth 44, 963–968 (1997). https://doi.org/10.1007/BF03011968
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DOI: https://doi.org/10.1007/BF03011968